The present invention relates to mechanical and chemical mechanical planarization of microelectronic substrates. More particularly, the present invention relates to controlling the pH of a microelectronic substrate during planarization and post-planarization processing of the microelectronic substrate.
Mechanical and chemical-mechanical planarization processes remove material from the surfaces of semiconductor wafers, field emission displays, and many other microelectronic substrates to form a flat surface at a desired elevation. FIG. 1 schematically illustrates a planarizing machine 10 with a platen or base 20, a carrier assembly 30, a polishing pad 41 positioned on the platen 20, and a planarizing liquid 44 on the polishing pad 41. The planarizing machine 10 can also have an under-pad 25 attached to an upper surface 22 of the platen 20 for supporting the polishing pad 41. In many planarizing machines, a drive assembly 26 rotates (arrow A) and/or reciprocates (arrow B) the platen 20 to move the polishing pad 41 during planarization.
The carrier assembly 30 controls and protects a substrate 12 during planarization. The carrier assembly 30 generally has a substrate holder 32 with a pad 34 that holds the substrate 12 via suction. A carrier drive assembly 36 typically rotates and/or translates the substrate holder 32 (arrows C and D, respectively). Alternatively, the substrate holder 32 can include a weighted, free floating disk (not shown) that slides over the polishing pad 41.
The combination of the polishing pad 41 and the planarizing liquid 44 generally defines a planarizing medium 40 that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The polishing pad 41 may be a conventional polishing pad composed of a polymeric material (e.g., polyurethane) without abrasive particles, or it may be an abrasive polishing pad with abrasive particles fixedly bonded to a suspension material. In a typical application, the planarizing liquid 44 may be a chemical-mechanical planarization slurry with abrasive particles and chemicals for use with a conventional non-abrasive polishing pad. In other applications, the planarizing liquid 44 may be a chemical solution without abrasive particles for use with an abrasive polishing pad. In any case, the planarizing liquid 44 can be pumped from a planarizing liquid supply 45 through a conduit 46, and through orifices 43 to a planarizing surface 42 of the polishing pad 41.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against the planarizing surface 42 of the polishing pad 41 in the presence of the planarizing liquid 44. The platen 20 and/or the substrate holder 32 then move relative to one another to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals of the planarizing medium 40 remove material from the surface of the substrate 12.
After the substrate 12 has been planarized, particulate matter, such as abrasive particles, particles removed from the polishing pad 41, and/or particles removed from the substrate 12 may adhere to the substrate. Accordingly, the substrate 12 can be rinsed to remove the particulate matter before the substrate 12 undergoes additional processing. One conventional approach to rinsing the substrate 12 is to pump a rinsing solution 53 from a rinsing solution supply 54 through the orifices 43 to the planarizing surface 42 of the polishing pad 41. The rinsing solution 53 rinses the substrate 12 while the substrate remains in situ on the polishing pad 41. The rinsing solution 53 may be introduced to the polishing pad 41 as the relative velocity between the substrate 12 and the polishing pad 41 is reduced or ramped down.
Another rinsing approach, which can be used in addition to or in lieu of the in situ approach discussed above, can include removing the substrate 12 from the polishing pad 41 with a substrate transporter 60 and moving the substrate 12 to a rinse chamber 50. The substrate transporter 60 can include a grasping device 62 that engages the substrate 12 after the substrate has been detached from the carrier assembly 30. The substrate transporter 60 can further include one or more movable arms 61 that can robotically move the substrate 12 to the rinse chamber 50. The rinse chamber 50 can include a plurality of opposing spray bars 51, each having a plurality of nozzles 52 for directing a spray of the rinsing solution 53 onto the substrate 12. The rinse chamber 50 shown in FIG. 1 can simultaneously accommodate two substrates 12 positioned upright in adjacent bays 57.
A third approach to removing particulate matter from the substrate 12 is to remove the substrate from the polishing pad 41 and place the substrate 12 on a separate buffing pad (not shown). The buffing pad then moves relative to the substrate and may also be supplied with a rinsing solution to convey the particulate matter away.
After the substrate 12 has been planarized and rinsed, the polishing pad 41 can be conditioned to restore its ability to planarize additional substrates. Accordingly, the planarizing machine 10 can include a conditioner 70 that removes polishing pad material from the planarizing surface 42 to expose new polishing pad material. The conditioner 70 can include an abrasive disk 71 for mechanically roughening the planarizing surface 42 of the polishing pad 41. The conditioner 70 can also include a conditioning fluid source 72 that supplies conditioning fluid to the polishing pad 41 for chemically conditioning the planarizing surface 42 of the polishing pad 41.
Planarizing processes must consistently and accurately produce a uniformly planar surface on the microelectronic substrate 12 to enable precise fabrication of circuits and photo-patterns. As the density of integrated circuits increases, the uniformity and planarity of the substrate surface is becoming increasingly important because it is difficult to form sub-micron features or photo-patterns to within a tolerance of approximately 0.1 microns on nonuniform substrate surfaces. Thus, planarizing processes must create a highly uniform, planar surface on the substrate.
One drawback with the conventional methods discussed above is that they may not create a sufficiently planer surface on the substrate because particulates may remain attached to the substrate as a result of contact between the substrate 12 and a variety of chemical solutions during and after planarization. For example, in one conventional method the planarizing solution is an ammonia-based solution, and the rinsing and conditioning fluids are deionized water. Each chemical solution may have different chemical characteristics and sequentially exposing the microelectronic substrate 12 to different chemical solutions may cause particulates to adhere to the surfaces of the substrate. These particulates may damage the wafer during subsequent polishing and handling steps, or may interfere with subsequent processing steps, such as masking and etching. Furthermore, the particulates may become incorporated into the devices formed on the substrate, potentially causing the devices to fail.
In the competitive semiconductor and microelectronic device manufacturing industries, it is desirable to maximize the throughput of finished substrates. Accordingly, a further drawback with the conventional processes, described above is that they may require additional time to remove the particulates from the substrate. The additional time can be required because the substrate has additional particulate adhered to it as a result of exposure to various chemical solutions.
The present invention is directed toward methods and apparatuses for processing a microelectronic substrate. In one embodiment, the apparatus can include a polishing pad having a planarizing surface and a source of planarizing liquid in fluid communication with the planarizing surface of the polishing pad. The microelectronic substrate is planarized by engaging the substrate with the polishing pad while the planarizing liquid is disposed on the polishing pad, and moving one of the substrate and the polishing pad relative to the other of the substrate and the polishing pad. As the relative motion between the substrate and the polishing pad is decreased, rinsing fluid having a pH approximately the same as a pH of the planarizing liquid can be introduced to the planarizing surface to maintain the pH of the microelectronic substrate at an approximately constant level.
In another embodiment, the microelectronic substrate can be removed from the polishing pad and rinsed remotely with a rinsing liquid having a pH approximately the same as a pH of the planarizing liquid. The rinsing liquid in either of the foregoing embodiments can be selected to include tetramethyl ammonium hydroxide and deionized water, or other substances where a pH of the rinsing liquid is approximately the same as the pH of the planarizing liquid.
In still another embodiment, the polishing pad can include a nonabrasive polishing pad and the planarizing liquid can include an abrasive slurry. The pH of the microelectronic substrate can be maintained by maintaining the pH of the abrasive slurry at an approximately constant level as the relative velocity between the microelectronic substrate and the polishing pad is reduced to approximately zero.
In yet another embodiment of the invention, the polishing pad can be conditioned by supplying to the polishing pad a conditioning liquid having a pH approximately the same as the pH of the planarizing liquid. In still a further embodiment, the microelectronic substrate can be cleaned by engaging the microelectronic substrate with the polishing pad, after the polishing pad has been conditioned, and moving at least one of the polishing pad and the substrate relative to the other of the polishing pad and the substrate.